Deck 9: Life and the Search for Habitable Worlds

Question 1

Suppose the inner edge of a star's habitable zone is at 2 AU.The star suddenly increases its luminosity by a factor of 4.Where is the inner edge of the habitable zone now?

A) 1 AU
B) 2 AU
C) 4 AU
D) 8 AU

Answer 1

4 AU

Question 2

How does the greenhouse effect change the habitability zone of a star?

A) It narrows the zone.
B) It does not affect the zone.
C) It moves the zone inward.
D) It moves the zone outward.

Answer 2

It moves the zone outward.

Question 3

Which of the following are all basic features of life as we presently understand it?

A) organic molecules, mutation, sexual reproduction
B) organic molecules, mutation, sensitivity
C) metabolism, sexual reproduction, mitosis
D) metabolism, organic molecules, competition

Answer 3

organic molecules, mutation, sensitivity

Question 4

Which of the following provides the basic energy source for some systems of life on Earth?

A) crystal stress
B) plant life
C) wind energy
D) geothermal energy

Question 5

Which of the following molecules is composed of amino acids?

A) DNA
B) RNA
C) proteins
D) all of the above

Question 6

Life is a process in the sense that:

A) all organisms reproduce.
B) all organisms go through a process of development over their lives.
C) most of its qualities are actions.
D) scientists are still coming to terms with its meaning.

Question 7

The figure below shows a molecule common in living cells,where the letters denote sugar and phosphate bases.What is the molecule?

A) RNA
B) DNA
C) amino acid
D) protein

Question 8

An exoplanet orbits its star on a circular orbit with a radius of 2 AU.If the planet is in the star's habitable zone,the star has a luminosity of:

A) 1 solar luminosity.
B) 2 solar luminosities.
C) 4 solar luminosities.
D) 16 solar luminosities.

Question 9

An example of an extremophile is a:

A) gamma-ray burst.
B) crab living inside an ecosystem powered by geothermal energy.
C) comet carrying organic molecules.
D) world outside the habitable zone that has liquid water.

Question 10

Which of the following is a basic feature of living things?

A) metabolism
B) composed of proteins
C) sexual reproduction
D) cell nuclei

Question 11

At present,conclusions about extraterrestrial life are based on:

A) lunar geology.
B) the chemistry of complex organic molecules in the interstellar medium.
C) the study of life on Earth.
D) telescopic signatures of life on exoplanets.

Question 12

Which of the following stellar properties affect the habitability of a planet surrounding the star?

A) luminosity
B) lifetime
C) magnetic fields
D) all of the above

Question 13

Scientists who study life on Earth in extreme conditions are most likely part of the field of:

A) exobiology.
B) astrobiology.
C) biophysics.
D) astrocology.

Question 14

Which of the following is part of the science of astrobiology?

A) telescopic studies of exoplanets
B) biochemical experiments on molecular self-replication
C) searches for extraterrestrial civilizations
D) all of the above

Question 15

Which of the following have been shown experimentally to be easy to produce in an environment similar to early Earth?

A) self-replicating molecules
B) proteins
C) amino acids
D) RNA

Question 16

Which of the following is a function of proteins inside cells?

A) structural components
B) enzymes
C) signalers
D) all of the above

Question 17

Why is liquid water considered essential for life to form?

A) Water is a highly effective solvent in biochemical reactions.
B) Most of Earth's surface is covered in water.
C) Liquid water defines the habitability zone.
D) Water is the key component of organic molecules.

Question 18

What basic characteristic of life is illustrated by the figure below?

A) metabolism
B) equilibrium
C) sensitivity
D) consumption

Question 19

Which discovery has challenged astronomers' methods in the search for extraterrestrial life?

A) radio astronomy
B) the greenhouse effect on Venus
C) bacterial colonies powered by radioactivity deep underground on Earth
D) water on comets

Question 20

Which Solar System world has challenged our understanding of habitable zones?

A) Enceladus
B) Earth
C) Mars
D) Io

Question 21

The Drake equation estimates the:

A) number of planets hosting life in the Milky Way.
B) number of technologically advanced civilizations in the Milky Way.
C) likelihood of observing a signature of life around a star.
D) likelihood of observing a radio signal from an extraterrestrial civilization.

Question 22

Self-replicating molecules:

A) can create copies of themselves.
B) have double-helix structures.
C) are composed of genes.
D) reproduce sexually.

Question 23

According to present understanding,what were the first self-replicating molecules to form on Earth?

A) amino acids
B) DNA
C) RNA polymers
D) RNA monomers

Question 24

In which part of the cell do mutations occur?

A) DNA
B) enzymes
C) RNA
D) proteins

Question 25

Lateral gene transfer is:

A) the swapping of genes by living organisms.
B) a synonym for natural selection.
C) the process through which genetic traits are expressed.
D) the first step in sexual reproduction.

Question 26

Of the following,which is the most UNCERTAIN factor in the Drake equation?

A) the average number of planets around a star
B) the average fraction of planets inside a star's habitable zone
C) the average lifetime of a star
D) the fraction of life-bearing planets on which intelligence evolves

Question 27

A lock requires a three-number sequence to open,with each number ranging from 1 to 10.If a thief requires three seconds to try any one combination,what is the maximum number of seconds before the thief opens the lock?

A) 3¹⁰
B) 10³
C) 3 × 10³
D) 10⁶

Question 28

Microorganisms and large animals differ in the:

A) nucleotides that make up their DNA.
B) physical structure of their DNA.
C) primary mechanism through which they pass genes to each other.
D) importance of natural selection to their evolution.

Question 29

Which of the following is a common way in which genes in a population change?

A) injury
B) aging
C) sexual reproduction
D) natural selection

Question 30

What fraction of Earth's life has the human species witnessed?

A) 10^-1
B) 10^-3
C) 10^-5
D) 10^-9

Question 31

According to the Miller-Urey experiment,which of the following is NOT a necessary ingredient of abiotic synthesis?

A) pressure
B) energy
C) water
D) organic molecules

Question 32

Experiments have shown that a mixture of methane,hydrogen,water,and free energy is likely to produce:

A) DNA.
B) RNA.
C) proteins.
D) amino acids.

Question 33

What most strongly controls the traits an organism displays?

A) genes
B) development
C) environmental stimuli
D) metabolism

Question 34

The smallest self-replicating RNA molecule is built from 24 nucleotides.How many such molecules could there be containing the same number of nucleotides?

A) 2²⁴
B) 4²⁴
C) 24²
D) 24⁴

Question 35

Why did the Miller-Urey experiment NOT correctly describe the construction of building blocks of prebiotic life?

A) There was much less radioactivity on the early Earth.
B) Water was not present on the early Earth.
C) Volcanism would have created a different atmosphere than used in the experiment.
D) none of the above

Question 36

Why did the oxygen content of the atmosphere increase dramatically 2.5 billion years ago?

A) The first life appeared on Earth.
B) The sea and earth became saturated with oxygen.
C) The Late Heavy Bombardment occurred.
D) The Cambrian explosion led to diverse plant life.

Question 37

Eukaryotic organisms became dominant after:

A) the Great Oxygenation Event.
B) the Cambrian explosion.
C) photosynthesis began.
D) the extinction of the dinosaurs.

Question 38

The development of antibiotic resistance among bacterial populations is a consequence of:

A) lateral gene transfer.
B) mutation.
C) natural selection.
D) all of the above.

Question 39

The figure below shows a phylogeny including many species of life on Earth.Which of the following pairs of organisms share the most recent last common ancestor?

A) diplomonads and entamoebae
B) ciliates and slime molds
C) vertebrates and fungi
D) animals and diplomonads

Question 40

Biologists refer to changes in a population's genetic distribution that result purely through random chance as:

A) natural selection.
B) genetic drift.
C) genetic evolution.
D) none of the above; such changes do not occur.

Question 41

What defines the habitability zone around a star?

Question 42

Why do astronomers search for signals of extraterrestrial intelligence at a wavelength of 21 centimeters?

A) At 21 centimeters there is very little contamination from other material in the galaxy.
B) Hydrogen emits radiation at 21 centimeters.
C) Oxygen emits radiation at 21 centimeters.
D) Greenhouse gases emit radiation at 21 centimeters.

Question 43

Which of the following questions expresses Fermi's paradox?

A) If extraterrestrial life exists, why is oxygen so rare in the Universe?
B) If extraterrestrial life exists, why is it not inside our Solar System?
C) If extraterrestrial intelligence exists, where should we search for it?
D) If extraterrestrial intelligence exists, why is it not here yet?

Question 44

What is sensitivity in the context of the definition of life?

Question 45

Which of the following signals do astronomers search for as part of the hunt for extraterrestrial intelligence?

A) dust scattering
B) X-ray flashes
C) optical lasers
D) gamma-ray bursts

Question 46

The figure below shows two different kinds of electromagnetic radiation traveling toward the observer at the left of the image.Which is more likely to reach the observer,and why?

A) A, because redshifting helps it propagate through dust.
B) B, because dust scatters short wavelength radiation most efficiently.
C) A, because high intensity radiation penetrates matter more efficiently.
D) B, because hydrogen produces long wavelength radiation.

Question 47

What is responsible for the oxygen in Earth's atmosphere?

Question 48

Why is carbon so well suited to forming the building blocks of life?

Question 49

How has the discovery of extremophiles changed our understanding of life in the universe?

Question 50

According to our present astronomical understanding,what astronomical environment is essential for life to begin and develop under evolution?

Question 51

A colleague explains to you that the origin of life seems implausible given the extremely small likelihood of producing self-replicating molecules in random chemical reactions.How could you answer this objection?

Question 52

An astronomical source is situated behind a thick cloud of hydrogen and dust.On its way to us ________ likely to be absorbed and scattered.

A) gamma rays are least
B) optical light is least
C) radio waves are least
D) all wavelengths are equally

Question 53

Which of the following factors does NOT appear in the Drake equation?

A) the number of stars in the Milky Way
B) the fraction of life-bearing planets on which intelligence evolves
C) the average lifetime of a technologically advanced civilization
D) the average delay between the formation of a planet and the appearance of life

Question 54

Which of the following provides a potential solution to Fermi's paradox?

A) It is safer for advanced civilizations to hide evidence of their existence.
B) There is insufficient time for advanced civilizations to travel across the Milky Way.
C) The radiation environment of the Milky Way prevents interstellar travel.
D) Dust blocks much of the Milky Way from view.

Question 55

What is the most important process in driving evolutionary adaptation?

Question 56

The Milky Way has 400 billion stars,and astronomers now believe that each one has about 3 planets around it.Which of the following additional pieces of information is necessary to estimate the number of technologically advanced civilizations in the Milky Way?

A) the speed at which such a civilization can expand
B) the average length of time over which life exists on a planet
C) the average lifetime of such a civilization
D) the number of stars colonized by such a civilization

Question 57

Describe the physical structure of a DNA molecule.

Question 58

What element produces radiation with a wavelength of 21 centimeters?

A) hydrogen
B) helium
C) carbon
D) oxygen

Question 59

How is information from an organism's genes used to construct enzymes for use in a cell?

Question 60

What wavelength regime is most commonly used in searches for extraterrestrial intelligence?

A) visible
B) ultraviolet
C) radio
D) X-ray

Question 61

The Drake equation begins with the number of stars in the Milky Way and requires five more pieces of information to estimate the number of technologically advanced civilizations in the Milky Way.Identify three of those additional factors.

Question 62

The figure below shows a timeline of life on Earth.Place the first appearance of the following organisms and processes on the timeline at the marked locations: eukaryotic cells,multicellular life,photosynthesis,and prokaryotic cells.

Question 63

What are the advantages of searching for extraterrestrial signals in the radio band?

Question 64

Using techniques similar to those employed by the Drake equation,estimate the number of "A" grades given out at your institution this semester.

Question 65

What is the "cosmic watering hole"?

Question 66

What is the most common method by which microorganisms acquire their genes?

Question 67

What are the four ways in which genes and their distribution within populations can change over time?

Question 68

What is one potential resolution to Fermi's paradox,if intelligent extraterrestrial life does exist?

Question 69

A colleague explains to you that the origin of life seems implausible given that producing the 192-nucleotide self-replicating RNA in our bodies would require longer than the age of the universe if created from scratch in random chemical reactions.How could you answer this objection?

Question 70

According to modern understanding,what does the Miller-Urey experiment tell us about the formation of life?